Desired performance objectives of personal care absorbent products include low leakage from the product and a dry feel to the wearer. However, absorbent products commonly fail before the total absorbent capacity of the product is utilized. An absorbent garment, for example a disposable diaper, often leaks at the leg, top front or top back areas of the diaper. Leakage can occur due to a variety of shortcomings in the product, one being an insufficient rate of fluid uptake by the absorbent system, especially on the second, third or fourth liquid surges.
It has been found that micturition can occur at rates as high as 15 to 20 milliliters per second and at velocities as high as 280 centimeters per second. Conventional diaper absorbent structures, such as those comprising admixtures of absorbent gelling particles and cellulosic fluffed pulp, may initially uptake fluid at rates of only about 8 milliliters per second or less, depending somewhat on the web density and concentration of gelling particulates. Even the rates for these fabrics can deteriorate once they have already received liquid surges into their structures. The above disparity between liquid delivery and uptake rates can result in excessive pooling on the surface of the fabric before it is taken up by the structure. In the meantime, pooled fluid can leak from the leg opening of the diaper and soil the outer clothing or bedding of the wearer.
Attempts to alleviate leakage include providing physical barriers with elastic leg gathers and changing the amount or configuration of the absorbent material at the zone of the structure into which the liquid surges typically occur. Absorbent gelling particles have also been included to increase the liquid holding capacity in various regions of the absorbent structure.
Absorbent articles have typically employed various types of absorbent pads composed of cellulosic fibers. For example, U.S. Pat. No. 3,523,536 to Ruffo discloses an absorbent fibrous web of predominantly shorter fibers intermixed with relatively longer fibers for purposes of stabilizing the web. U.S. Pat. No. 3,768,118 to Ruffo, et al. relates to a process for blending longer and shorter fibers. U.S. Pat. No. 3,663,348 to Liloia, et al. discloses an absorbent product in which a disclosed fabric serves as a body side, fluid pervious liner material, and an absorbent core includes a loosely compacted cellulose batt with a densified layer on one side.
Particular absorbent garments have been configured to control the distribution of absorbed liquids. U.S. Pat. No. 4,578,070 to Holtman discloses incontinence pads which include a bilayer, corrugated nonwoven structure. U.S. Pat. No. 4,681,577 to Stern and Holtman discloses incontinence pads placed in a liquid-impermeable, flexible shell. The absorbent structure disclosed in the '577 patent includes either a corrugated or uncorrugated version of the bilayer nonwoven structure disclosed in the '070 patent, located in the front portion of the product. A second resilient, open structure, such as a resilient nonwoven or open cell foam, in the back portion is further disclosed for the purpose of providing fecal waste containment.
U.S. Pat. No. 4,699,619 to Bernardin discloses another cellulosic absorbent structure which can comprise a multi-layer core arrangement wherein a top layer has a greater pore size than that of an underlying layer. The pore size gradient between the core layers can be achieved in various ways, for example, by using webs of different densities or webs with a common density but formed from fibers of different sizes. A portion of superabsorbent material can also be placed at various locations within the absorbent structure.
European Application No. 254,476 of Alemany et al. discloses an absorbent member having fluid storage and acquisition zones composed of cellulosic fluff mixed with absorbent gelling particles. The particles are purportedly used to keep the fibrous structure from collapsing when wet. The acquisition zone has a lower density and lower basis weight than that of the storage zone. U.S. Pat. No. 4,673,402 to Weisman, et al. discloses a dual-layer absorbent core arrangement comprising a bottom fluff pad containing hydrogel particles, and a top fluff pad with little or no hydrogel particles.
Non-woven materials such as carded webs and spun-bonded webs, have been used as the body-side liners in absorbent products. Specifically, very open, porous liner structures have been employed to allow liquid to pass through them rapidly, and help keep the body skin separated from the wetted absorbent pad underneath the liner. In addition other layers of material, such as those constructed with thick, lofty fabric structures, have been interposed between the liner and absorbent pad for the purpose of reducing wet-back.
With conventional fluff-based absorbent structures, such as those discussed above, the cellulosic fibers, when wetted, can lose resiliency and collapse. As a result, the liquid uptake rate of the wetted structures may become too low to adequately accommodate subsequent, successive liquid surges. Where absorbent gelling particles are incorporated between the fibers to hold them apart, the gelling particles swell and do not release the absorbed fluid. Swelling of the particles can then diminish the void volume of the absorbent structure and reduce the ability of the structure to rapidly uptake liquid.
The addition of more absorbent material, e.g., secondary fluff pledgets, or absorbent gelling particles has been employed to increase holding capacity. The desired rate of liquid intake within such arrangements, however, may not be sufficiently, sustained during successive liquid surges.
Despite the development of absorbent structures of the types surveyed above, there remains a need for improved absorbent structures which can adequately reduce the incidence of leakage from absorbent products, such as disposable diapers. There is a need for an absorbent structure which can provide improved handling of liquid surges and more effectively uptake and retain repeated loadings of liquid during use.